The goal is to determine what kind of molecules contribute to ionic permeability of nerve and muscle membranes. Ionic currents of single myelinated nerve fibers and skeletal muscle fibers will be studied under voltage clamp conditions to determine the electrical properties of electrically excitable sodium channels and potassium channels and of the acetylcholine-sensitive channel of the endplate. Experiments are designed to reveal the kinetics of the gating processes; to determine the dimensions and energy barriers to ion movements inside the channels; and to determine the chemical nature of functionally important groups on the channel macromolecule. Theories will be developed to explore further the properties of pores.